Neuromodulation
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In neuroscience, '''neuromodulation''' is the process in which several classes of [[neurotransmitters]] in the nervous system regulate diverse populations of [[neurons]] (one [[neurons|neuron]] uses different [[neurotransmitters]] to connect to several [[neurons]]), as opposed to direct [[synapse|synaptic transmission]] in which one presynaptic neuron directly influences a postsynaptic partner (one [[neuron]] reaching one other [[neuron]]), neuromodulatory transmitters secreted by a small group of neurons diffuse through large areas of the nervous system, having an effect on multiple neurons. Examples of neuromodulators include [[dopamine]], [[serotonin]], [[acetylcholine]], [[histamine]] and others.
A neuromodulator is a relatively new concept in the field and it can be conceptualized as a [[neurotransmitter]] that is not reabsorbed by the pre-synaptic neuron or broken down into a [[metabolite]]. Such neuromodulators end up spending a significant amount of time in the CSF ([[cerebrospinal fluid]]) and influencing (or modulating) the overall activity level of the [[brain]]. For this reason, some [[neurotransmitters]] are also considered as [[neuromodulators]]. Examples of neuromodulators in this category are [[serotonin]] and [[acetylcholine]].
==Neuromuscular systems==
Neuromodulators may alter the output of a physiological system by acting on the associated inputs (for instance, [[central pattern generator]]s). However, modeling work suggests that this alone is insufficient,<ref name="Stern">{{cite journal | last =Stern | first =E | authorlink = | coauthors =Fort TJ, Millier MW, Peskin CS, Brezina V | title = Decoding modulation of the neuromuscular transform| journal =Neurocomputing | volume =| issue =6954 | pages = | publisher = | date =2007 | url =http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V10-4M9Y1V1-8&_user=489277&_coverDate=11%2F11%2F2006&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000022679&_version=1&_urlVersion=0&_userid=489277&md5=7d1066d0824172ae9521c974325c076a#bcor1 | doi =10.1016/j.neucom.2006.10.117 | id = | accessdate =2007-04-07}}</ref> because the neuromuscular transformation from neural input to muscular output may be tuned for particular ranges of input. Stern et al. (2007) suggest that neuromodulators must act not only on the input system but must change the transformation itself to produce the proper contractions of muscles as output.<ref name="Stern" />
==Diffuse modulatory neurotransmitter systems==
Neurotransmitter systems are systems of [[neurons]] in the brain expressing certain types of [[neurotransmitters]], and thus form distinct systems. Activation of the system causes effects in large volumes of the brain, called ''volume transmission''.
The major neurotransmitter systems are the [[noradrenaline]] (norepinephrine) system, the [[dopamine]] system, the [[serotonin]] system and the [[cholinergic]] system. Drugs targeting the neurotransmitter of such systems affects the whole system, and explains the mode of action of many drugs.
Most other neurotransmitters, on the other hand, e.g. [[glutamate]], [[GABA]] and [[glycine]], are used very generally throughout the central nervous system.
===Comparison===
{| class="wikitable"
|+Neurotransmitter systems
|-
! System !! Origin!!<ref name=Rang> Unless else specified in boxes, then ref is: {{cite book |author=Rang, H. P. |title=Pharmacology |publisher=Churchill Livingstone |location=Edinburgh |year=2003 |pages= page 474 for noradrenaline system, page 476 for dopamine system, page 480 for serotonin system and page 483 for cholinergic system. |isbn=0-443-07145-4 |oclc= |doi=}} </ref> Targets!!<ref name=Rang/> Effects<ref name=Rang/>
|-
!rowspan=2| Noradrenaline system
| [[locus coeruleus]] || [[adrenergic receptors]] in:
*[[spinal cord]]
*[[thalamus]]
*[[hypothalamus]]
*[[striatum]]
*[[neocortex]]
*[[cingulate gyrus]]
*[[cingulum]]
*[[hippocampus]]
*[[amygdala]]
|rowspan=2|
*arousal
*[[reward system]]
|-
| [[Lateral tegmental field]] ||
*[[hypothalamus]]
|-
! Dopamine system
|| [[dopamine]] [[neural pathway|pathways]]:
* [[mesocortical pathway]]
* [[mesolimbic pathway]]
* [[nigrostriatal pathway]]
* [[tuberoinfundibular pathway]]
|| [[Dopamine receptor]]s at pathway terminations.
|| [[motor system]], [[reward system]], [[cognition]], [[endocrine]], [[nausea]]
|-
!rowspan=2| Serotonin system
| caudal [[dorsal raphe nucleus]] || [[Serotonin receptors]] in:
*[[deep cerebellar nuclei]]
*[[cerebellar cortex]]
*[[spinal cord]]
|rowspan=2| Increase ([[extraversion and introversion|introverson]]), [[Mood (psychology)|mood]], [[satiety]], [[body temperature]] and [[sleep]], while decreasing [[pain and nociception|nociception]].
|-
| rostral [[dorsal raphe nucleus]] || [[Serotonin receptors]] in:
*[[thalamus]]
*[[striatum]]
*[[hypothalamus]]
*[[nucleus accumbens]]
*[[neocortex]]
*[[cingulate gyrus]]
*[[cingulum]]
*[[hippocampus]]
*[[amygdala]]
|-
!rowspan=3| Cholinergic system
| ''pontomesencephalotegmental complex'' || (mainly) [[M1 receptor]]s in:
*[[brainstem]]
|rowspan=3|
*[[learning]]
*[[Memory#Short-term|short-term memory]]
*arousal
*reward
|-
| [[basal optic nucleus of Meynert]] || (mainly) [[M1 receptor]]s in:
*[[neocortex]]
|-
| medial [[septal nucleus]] || (mainly) [[M1 receptor]]s in:
*[[hippocampus]]
*[[neocortex]]
|}
===Noradrenaline system===
''Further reading: [[Norepinephrine#Norepinephrine system]]''
The noradrenaline system consists of just 1500 neurons on each side of the brain, which is diminutive compared to the total amount of more than 100 billion neurons in the brain. Nevertheless, when activated, the system plays major roles in the brain, as seen in table above. [[Noradrenaline]] is released from the neurons, and acts on [[adrenergic receptors]].
===Dopamine system===
''Further reading: [[Dopamine#Functions in the brain]]''
The dopamine system consists of several pathways, originating from the [[ventral tegmentum]] or [[substantia nigra]] as examples. It acts on [[dopamine receptors]].
[[Parkinson's disease]] is at least in part related to failure of dopaminergic cells in [[deep-brain nuclei]], namely the [[substantia nigra]]. Treatments potentiating the effect of dopamine precursors have been proposed and effected, with moderate success.
====Pharmacology====
* [[Cocaine]], for example, blocks the reuptake of [[dopamine]], leaving these neurotransmitters in the [[synapse|synaptic gap]] longer.
* [[AMPT]] prevents the conversion of tyrosine to [[L-DOPA]], the precursor to dopamine; [[reserpine]] prevents dopamine storage within [[vesicles]]; and [[deprenyl]] inhibits [[monoamine oxidase]] (MAO)-B and thus increases dopamine levels.
===Serotonin system===
''Further reading: [[Serotonin#Gross anatomy]]''
The serotonin system in the CNS contains only 1% of total body serotonin, the rest being found as transmitters in the [[peripheral nervous system]]{{Fact|date=March 2008}}. It travels around the brain along the [[medial forebrain bundle]] and acts on [[serotonin receptors]]. In the [[peripheral nervous system]] (such as in the gut wall) serotonin regulates vascular tone.
====Pharmacology====
* [[Prozac]] is a [[serotonin reuptake inhibitor|selective serotonin reuptake inhibitor]] (SSRI), hence potentiating the effect of naturally released serotonin.
===Cholinergic system===
''Further reading: [[Acetylcholine#in CNS]]''
The cholinergic system works primary by [[M1 receptor]]s, but [[M2 receptor|M2-]], [[M3 receptor|M3-]], [[M4 receptor|M4-]] and [[M5 receptor]]s are also found in the CNS.
===Others===
The [[gamma-aminobutyric acid]] (GABA) system is more generally distributed throughout the brain. Nevertheless, it has an overall inhibitory effect.
*[[Opioid peptides]] - these substances block nerve impulse generation in the secondary afferent pain neurons. These peptides are called opioid peptides because they have opium-like activity. The types of opioid peptides are:
**[[Endorphins]]
**[[Enkephalins]]
**[[Dynorphins]]
*[[Substance P]]
*[[Octopamine]]
==Other uses==
Neuromodulation also refers to a medical procedure used to alter nervous system function for relief of pain. It consists primarily of electrical stimulation, lesioning of specific regions of the nervous system, or infusion of substances into the cerebrospinal fluid. Electrical stimulation are devices such as [[Spinal Cord Stimulator]]s (SCS) (surgically implanted) or [[Transcutaneous Electrical Nerve Stimulator]]s (TENS) (external device).
==References==
{{Reflist}}
==External links==
*[[North American Neuromodulation Society]]
*[http://serendip.brynmawr.edu/bb/neuro/neuro98/202s98-paper2/Casasanto2.html Neuromodulation and Neural Plasticity]
*[http://www.neuromodulation.com International Neuromodulation Society]
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[[Category:Brain]]
[[Category:Central nervous system]]
[[Category:Neuroanatomy]]
[[Category:Organs]]
[[Category:Neurochemistry]]
[[Category:Neurology]]
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